Chronic pain, which may be defined as pain that persists or recurs for longer than 3 months, is not uncommon in the obstetric population. The physiological stresses of pregnancy, such as musculoskeletal or pelvic girdle strain, may trigger a chronic pain disorder or exacerbate a pre-existing one. Chronic pain in the parturient poses particular challenges to the maternity team and has significant implications for both maternal and fetal wellbeing.
Problems and special considerations
Management of women with chronic pain may be hindered by a lack of awareness among maternity staff of the medical and pharmacological issues involved, such that patients may be denied effective analgesia or placed at risk if monitoring is inadequate. If there is a background of drug misuse, this situation may be compounded by any underlying psychological issues on the part of the mother, and/or by any judgemental attitudes on the part of the staff.
Women with chronic pain syndromes may be on long-term opioids and/or adjuvant medication. Long-standing opioid therapy may cause tolerance and/or hyperalgesia, and hence these women may experience difficulty with the control of postpartum pain and are likely to require higher doses of postoperative analgesia - which may be up to five times higher than in their opioid-naive counterparts. Despite exhibiting tolerance to some opioid- related side effects, these patients remain at risk of respiratory depression, particularly with escalating opioid requirements in the peripartum period.
Chronic opioid use is associated with adverse obstetric and neonatal outcomes including miscarriage, fetal growth restriction and placental abruption. Sudden interruption of opioid intake may lead to the development of acute withdrawal syndrome in the mother, which manifests as agitation, haemodynamic changes and uterine contractions. Infants who have been chronically exposed to opioids in utero may suffer with neonatal abstinence syndrome after birth.
Some women with neuropathic pain disorders that are refractory to conventional pharmacological or surgical treatment may require the placement of a spinal cord stimulator (SCS) or an intrathecal drug delivery device. The former consists of a pulse generator and electrode leads that are placed in the epidural space and acts by delivering electrical stimulation to the dorsal column, thus reducing the perception of pain, while the latter consists of an indwelling intrathecal catheter and an external or implantable pump that enables the delivery of a fixed or variable dose of drug. The presence of these devices has implications for regional anaesthesia as there is a risk of damage to the leads or catheter by the regional block needle or epidural catheter, or introduction of infection. In addition, previous instrumentation of the epidural space for device placement may result in scarring, with subsequent failed or patchy epidural analgesia.
Management
The successful peripartum management of women with chronic pain disorders should be a multidisciplinary effort and must include input from a specialist pain team and neonatol- ogist. Antenatally, a plan should be made and referral routes established in case acute intervention is required at any time during pregnancy or postpartum.
As a rule, baseline opioid maintenance therapy should continue throughout labour and delivery. Antenatal involvement of an acute pain specialist can help to form a strategy. Multimodal analgesia should be utilised, and adjuvant drugs such as ketamine may be useful to supplement opioid therapy in the postoperative period. Abdominal field blocks such as a transversus abdominis plane (TAP) block may be used to supplement parenteral analgesia after caesarean section, although their reported efficacy in opioid-dependent parturients is variable. These patients should be closely monitored for respiratory depression, and some may best be observed in a high-dependency setting in the postnatal period.
In parturients with an implanted pain management device, the location of the leads or catheter must first be verified before attempting regional anaesthesia, in order to minimise the risk of damage to the device’s components. Post-implantation images should be obtained, and antenatal consultation with the chronic pain or neurosurgery team is required. Where previous images of the spine cannot be acquired, ultrasound guidance may be used to confirm the position of the leads and guide insertion. Strict procedural asepsis is particularly important, and must be observed and clearly documented. An SCS is sensitive to the electromagnetic interference that may be generated by the use of diathermy, so appropriate precautions, similar to those taken with cardiac implantable electronic devices, must be observed to reduce this (see Chapter 92, Arrhythmias).
It is recommended that the baseline infusion rate of an intrathecal pump remains active during labour and delivery alongside regional analgesia. Utilisation of the access port to administer spinal anaesthesia is generally not advised; if it were to be used, then initial aspiration of the intrathecal catheter must be performed, to dispose of the drug in situ. If epidural placement is attempted, the point of entry should avoid the site of the dural puncture.
Key points
• Pregnant women on treatment for chronic pain syndromes are at risk of adverse maternal and fetal outcomes.
• Opioid maintenance therapy should be continued throughout the peripartum period.
• Chronic opioid therapy is unlikely to provide useful analgesia, and should be considered a patient’s baseline; multimodal analgesic regimens with significant additional opioid administration are likely to be required.
• High-dependency monitoring may be necessary.
• The presence of an implanted pain management device requires special precautions with the performance of neuraxial blocks and the use of diathermy.
• Multidisciplinary input is required at intervals throughout pregnancy and postpartum.
Further reading
Sommerfield D, Hu P, O’Keeffe D, McKeating K. Caesarean section in a parturient with a spinal cord stimulator. Int J Obstet Anesth 2010; 19: 114-17.
Souzdalnitski D, Snegovskikh D. Analgesia for the parturient with chronic nonmalignant pain. Tech Reg Anesth Pain Manag 2014; 18: 166-71.
Young AC, Lubenow TR, Buvanendran A. The parturient with implanted spinal cord stimulator: management and review of the literature. Reg Anesth Pain Med 2015; 40: 276-83.
Young JL, Lockhart EM, Baysinger CL. Anesthetic and obstetric management of the opioid-dependent parturient. Int Anesthesiol Clin 2014: 52: 67-85.